d-2-(6-Methoxy-2-naphthyl)-propionic acid is a known substance having antiphlogistic, analgesic and antipyretic properties; it is described in U.S. Pat. No. 3,904,682. Several methods for its preparation are also known but in general, they are not stereospecific in that they first contemplate the synthesis of a racemic mixture of the d- and l-2-(6-methoxy-2-naphthyl)-propionic acids, which is subsequently resolved into the two optical antipodes through formation of salts with optically active organic bases, taking advantage from the different solubilities of the salts of the two isomers d and l with said bases in a suitable solvent (see, for instance, German application Nos. 1,934,460; 2,005,454; 2,013,641 and 2,159,011; U.S. Pat. Nos. 3,658,858 and 3,658,863.